1. Field of the Invention
The present invention relates to electrochemical drilling and, more particularly, to an improved electrode assembly and machine for use in drilling small diameter holes.
2. Description of the Prior Art
Electrochemical drilling is a widely used technique for providing holes and the like in difficult to machine metal and alloy articles, such as nickel or cobalt base superalloy turbine blades or vanes. U.S. Pat. No. 3,647,674 discusses several factors which limit the minimum diameter of holes which can be drilled with such processes.
One limiting factor which has been especially troublesome is the propensity for blockage of the hollow electrode tube by dirt particles or other matter in the electrolyte being pumped therethrough. Of course, if electrolyte flow through the tube is blocked, drilling cannot proceed and the tube must be removed and cleaned before drilling can resume. In some cases, this necessitates dismantling major parts of the electrochemical machine, such as, for example, the electrolyte manifold which distributes electrolyte to the individual electrode tubes.
As the diameter of the hole to be drilled decreases, the internal diameter of the hollow electrode tube in general must also decrease. As a result, clogging and blocking of the tube is considerably more frequent in drilling smaller diameter holes than larger ones and this increased clogging has somewhat limited the use of electrochemical drilling in the commercial production of large numbers of parts having a plurality of small diameter holes therein. The problem is aggravated when the holes are not only small in diameter but also of considerable depth.
Another problem associated with small hole drilling is that the thin walled, small diameter electrode tubes are prone to bend and flex during drilling and thereby deviate from the desired drilling path. This bending produces misaligned holes and is aggravated as the depth of the hole increases.